Today, off-highway trucks are used to mine many minerals for further refining and clay type overburden or cover materials. The mining of various types of materials is relatively straightforward, although the complexity of the mining is increased by 1) the natural cohesive characteristics of many materials, 2) the amount of material being mined/hauled and 3) the environmental conditions under which it is mined.
In their natural state, many mined materials are extremely sticky and these mined materials naturally freely cling to each other. For example, the composition of oil sands, oil sands overburden and oil sands cover material is, by its very nature, extremely oil and sticky. The specific composition of oil sands is: 1) a grain of sand, 2) surrounded by or encapsulated by moisture/water, and 3) oil which encapsulates and surrounds both the grain of sand and the water. The surrounding oil of each grain causes the oil sands to cling to each other and surfaces the oil sands contact. The sticky nature of certain materials, such as oil sands, The sticky nature of certain materials, such as oil sands, can result in a buildup of material on the truck body surfaces, etc. that contact such materials. For example, walking around on some materials will quickly result in the soles of a person's shoes building up with layers of material that can easily buildup to 8 to 10 mm thick.
This same sort of buildup happens in truck bodies. A common condition that occurs during the use of truck bodies is the buildup of “carryback.” As successive loads are hauled, sticky hauled material begins to incrementally buildup in the interior of the body with each load until the body retains a significant amount of material between successive loads. Experience has shown that initial load carryback begins in those areas of a truck body where intersecting walls of a truck body meet.
This build up of material or “carryback” is significant for very sticky materials. The characteristics of materials which stick together and coagulate are exacerbated as material in its natural state is disturbed by the mining process. With these sorts of materials, the buildup of carryback happens quickly and is significant. This significant carryback reduces the effective capacity of the truck body and reduces the efficiency of the truck and the overall mining operation.
Mine loading shovels weigh in at 1450 to 1800 tons and off-highway trucks weigh in at 550 to 600 tons. As loading shovel buckets dig into the materials being mined and load or “drop” 100 tons at a time of material into off-highway truck bodies, the materials are further compressed in the off-highway truck body. Also, as material is hauled in an off-highway truck body the material is further compacted as off-highway trucks navigate the mine haul roads to their destination, vibrating the load, causing settling of the load in the off-highway truck body. By the time an off-highway truck reaches its destination, in some cases the shaking and resulting settling of the hauled load results in the hauled materials amalgamating into almost a solid packed mass.
The circumstances of mining and hauling, in combination with the cohesive coagulating characteristics of some hauled materials, can result in the hauled materials dumping from the truck body as a solid mass or “loaf.” As loads of material “loafs” exit truck bodies, the truck chassis itself is subjected to extreme ‘jolts,’ resulting in severe truck driver discomfort. Drivers of trucks hauling materials which “loaf” are often exposed to extreme ‘whole body vibration’ as loads of “loafs” are dumped.
The average individual is unlikely to appreciate the impact that the problems associated with mining and hauling cohesive materials has, as most individuals are unaware of the amount of cohesive materials that are being mined. Considering only the example of oil sands, the shear amount of this material being mined today is almost beyond comprehension for the average individual. Today, about every two (2) tons of oil sands mined produces about one (1) barrel of oil. Current production of oil from surface mining operations in the Northern Alberta Region of Canada, alone, is about 750,000 barrels of oil a day, which translates to the daily mining of one and a half million tons of oil-producing oil sands. This number does not include any oil sands overburden or cover materials that must also be mined to expose the oil sands.
By comparison, the Hoover Dam spanning the Colorado River required 3,250,000 cu. yards (2.6 million cu. m.) of concrete, which has been compared to the amount of concrete in a 16-ft. wide (4.9 m) highway between Pensacola, Fla., and Seattle, Wash. Putting this into perspective, enough oil bearing sands material is mined/hauled today to recreate a new Hoover Dam about every four days. Mining oils sands is a massive endeavor.
The environmental conditions for mining oil sands are extremely challenging. Today, the bulk of oil sands mining occurs in Northern Alberta, Canada. In this region of the world, temperatures in the winter months can get very cold, approaching minus 40 degrees Celsius (about −40° Fahrenheit). But in the summer months, temperatures often exceed 35 degrees Celsius (+95° Fahrenheit), resulting in the oils sands having a semi-fluid, sticky and goby consistency. Although the oil sands are very oily in composition, as they are mined, they tend to re-solidify in a truck body to a very firm single mass (“loaf”), which invariably may tend to stick to the inner surface of the truck body. In either climate, though, as loads of oil sands material are dumped from a truck body, an oils sands ‘loaf’ is created. And, yet a clean release of the material from the inner surface of a truck body can be problematic. Transporting oil sands material is virtually unknown outside the localized mining of oil sands.